Ray counter



Dec. 28, 1948.

Filea Jan. 2, 1948 Fig. 2

H. METTEN EI'AL 2,457,781

RAY COUNTER 2 She'ets-Sheet 1 Herbert Metteu Frederic Kourg INVENTORS by 2 Z G ATTORNEY Dec. 28, 1948. H. METTEN ETAL 2,457,781

' RAY COUNTER Filed Jan. 2, 1948 2 Sheets-Sheet 2 Herbert Metten Frederic Kourg now --f522322 0,709.78 8.70 sun/I09 121v INVENTORS Anoauzv the inside of the disc II, at its center through which a Patented o. 28, 1948 RAY coma-En Herbert Metten, Boston, and Frederic Koury,

Somerville, Masa, asslgnors to Sylvania Electric Products Inc., Sal

of Massachusetts em, Mass... a corporation Application January 2, 1948, Serial No. 94 8 Claims. (Cl. 250-275) This invention relates to ray detection tubes, for example so-called Geiger-Mueller counter tubes, and particularly to such tube for detection of gamma rays.

- An object of the invention is a counter tube with increased sensitivity. This object is attained by the use of an annular disc type of counter, in which the discs are plated with bismath, and particularly with a layer of bismuth in a critical thickness range.

Further objects, advantages and features of the invention will be apparent from the following specification, taken in conjunction with the accompanying drawings, in which:

Figure 1 is a longitudinal section of a device according to the invention;

Figure 2 is a top view thereof;

Figure 3 is a view, partly in section, of one of the annular discs according to the invention; and

Figure 4 is a graph of the coating thickness'vs. the sensitivity of the device.

.In Figure 1, the metal tube I has the end cap 2 fitted to one of its ends, the cylindrical walls 3 of said cap being fitted inside the tube I and hermetically sealed thereto. The other end of the tube I is sealed by an end cap 4, but at a point removed from the extremity 5 of the tube I. An exhaust tube 6 is hermetically sealed into end cap 0, and the glass wafer or stem 1 is sealed to said end cap 4 through the intermediary of a Kovar metal cylinder and a flanged cylindrical metal piece as shown, the seal being, of course, hermetic.

The lead-in wire 8, sealed through the glass stem I, ends in the hook 9. Near, but spaced from, the other end of the tube I is annular disc I0, at the center of which is the insulating disc II, of glass or ceramic, for example, flanged to fit and having a hole I! wire I2 may be passed with some clearance. The insulating disc II has the cylindrical hub I3 around which is fitted a collar I4 with tabs I5 from which the spring wire I6 is bent over the hole I! and a1- fixed to wire I2, the other end of which is atfixed to hook 9. The spring wire I0 holds the central wire I2 reasonably taut. The wire I2 may be. of tungsten, for example, and forms the anode of the device.

The lead-in wire 8 and its hooked end 9 are set in a glass tube 20 extending from stem 1 to a position somewhat in advance of the hooked end 9. The annular disc III has holes 2| therein, to facilitate exhaust.

For example. and not by way of limitation, the tube I may be about 2 inches in diameter, with a space of about an inch between end cap 2 and disc I0, and a spacing of about inch between the annular discs I 8, which may have a central opening about half an inch. The wire I2 may be of 0.003 inch diameter. The distance between end caps 2 and 4 may be about 4%11101'185. For this particular tube, the drawing is to full scale. The tube has a suitable gas filling.

The annular discs I8 may be of copper, for example, and about 0.008 inch thick, with a bismuth plating about 0.005 to 0.008 inch in thickness. This plating is critical in thickness as shown in Figure 4, the greatest number of net counts per second occurring at about 0.0065 inch thickness of plating. This net count number is nearly greater than that with plain 0.031 inch lead annular discs.

For plating, we have used a solution of 25 grams bismuth trioxide in cc. of 70% perchloric acid, C. P. This is agitated six hours until a colorless solution is formed, and then gradually diluted to one liter with distilled water. As anodes, we used C. P. bismuth metal powder poured into a graphite boat and fired in a hydrogen atmosphere at 800 C. for 15 minutes.

Annular discs of copper or other suitable metal were prepared by degreasing and then soaking in 50% nitric acid solution and then being put in an acid bright dip for 30 seconds. The cleaned discs were then mounted on a clip type plating rack immersed in the plating solution, and plated at a current density of 3 to 9 amperes per square foot for about 16 hour During plating the parts were agitated with an up and down motion at a rate of about 40 cycles per minute.

After plating the discs were rinsed, treated with 50% nitric acid solution for 30 seconds, then rinsed in water, dried and immediately mounted into the ray detector tube.

The plated surface should be free of stains and bright, with the metallic bismuth deposits of a fine crystal structure, as the density of the Y plated bismuth Is important for the sensitivity of the tube. The density by our plating method is about 0.9 gram per c. c.

The graph-or Figure 4 is for a tube as described with a self quenching gas fill, operated at 960 volts in series with a 5 megohm resistor. The tube was tested with an unfiltered radium source 12 inches from the end of the counter. The tube had a starting voltage of about 840 volts with a minimum plateau of volts and a plateau slope of 0.4% per volt rise, over this range.

This tube is several times as sensitive as the conventional concentric cylinder type.

The tube will ordinarily be filled with gas at some convenient pressure, generally about 10 cm. A fill of argon with 0.01% bromine may be used for operating at a lower voltage than that given above. A fill of neon at 20 centimeters of mercury pressure, with the addition, at 0.25 cm. pressure, of a 4 parts argon and 1 part chlorine mixture, is especially good. The tube described in detail herein as an example of a specific embodiment of the invention was filled with about 9 cm. (of mercury) pressure of argon, and 0.7 cm. pressure of propane, and had 14 discs.

In Figure 3 the copper disc is shown with the plated bismuth layer 22 thereon.

What we claim is:

1. In a ray counter tube having a gas filling and an anode, a cathode comprising a bismuth-plated annular metal disc.

2. In a ray counter tube having a gas filling and an anode, a cathode comprising an annular metal disc having a plating of bismuth between 0.005 and 0.008 inch thick.

3. In a ray counter tube having a gas filling and an anode, a cathode comprising an annular metal disc having a plating of bismuth about 0.0065 inch thick.

4. In a ray counter tube having a gas filling and an anode, a cathode of bismuth substantially 0.0065 inch thick.

5. A gamma ray counter tube comprising a sealed metal envelope, 9, wire anode along the axis thereof and insulated therefrom, and a series oi bismuth-plated annular discs coaxial with said wire and in contact with said envelope.

6. In a gamma ray counter tube having a gas filling and an anode, an annular copper disc plated with: bismuth to a thickness of about 0.0065 inch.

7. A gamma ray counter tube comprising a sealed metal envelope, a wire anode along the axis thereof and insulated therefrom, a series of bismuth-plated annular discs coaxial with said wire and in contact with said envelope, and a gas filling at a pressure of about 10 cm. of mercury therein, said gas filling comprising argon with about 0.01% bromine.

8. In a ray counter tube having a gas filling and an anode, a metal cathode having a plating of bismuth about 0.0065 inch thick.

HERBERT METTEN. FREDERIC KOURY.

' file of this patent:

UNITED STATES PATENTS Number 

